Ignition system



E. F. w. ALEXANDERSON 1,723,908

IGNITION SYSTEM Filed June 14, 1926 Figl. 2 3 4 Invcantow: E'nns'li FTAlexandewson,

His Atll'owmay.

Patented Aug. 6, 1929.

UNITED STATES PATENT OFFICE.

ERNST F. W. ALEXANDERSON, 0F SCHE-NECTADY, NEW YORK, ASSIGNOR 1'0GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

IGNITION SYSTEM.

Application filed June 14,

My present invention relates to ignition systems of the general type in.which a gas or vapor is ignited by means of an are or spark dischargepassing acrossa discharge a g It is well known that when a dischargetakes place across a gap between two electrodes, high frequencyoscillations will be produced in the circuit connected to theelectrodes, the frequency of the oscillations being dependent upon theconstants of the circuit. Much trouble has been experienced with suchsystems in the past because of the fact that the high frequency currentspro-- duced in this way have interfered with radio reception in the nearneighborhood, or even at some distance from the point at which thedischarge takes place due to the high frequency currents being suppliedto the distribution circuit by means of which current is supplied to thedischarge gap.

Such systems usually include a step-up transformer connected to acomparatively low potential alternating distribution system. Unlessmeans is taken to prevent it, the high frequency currents may besupplied through the transformer to the distribution system anddistributed over a considerable area to such an extent as to interferewith the operation of radio receivers. This type of interference may bedue to radiation of high frequency energy from the distribution system,or to inductive effects which may be present when the radio receiver islocated near a conductor of the distribution system. Disturbance mayalso be caused by radiation of high frequency energy from the highpotential conductors connecting the transformer and the discharge gap.The object of m invention is to provide a s stem in whic both forms ofdisturbance with radio reception may be prevented.

The first form of disturbance may be largely minimized b rovidinsuitable chokes or filters in t e ow tension distri bution systemclosely adjacent the transformer. The second form of disturbance issomewhat more difficult to avoid. If the leads connecting the highpotential windings of the transformer and the discharge gap are closelyadjacent one another and parallel it would appear that radiation fromthe two leads would be neutralized since the current at any instant isflowing in oppo- 1926. Serial No. 115,769.

site directions in the two leads. I have found, however, that in actualpractice it is very difficult to provide a system in which thistheoretical condition is obtained. If the capacities between the twoconductors and ground are unequal then a greater amount of radiationwill take place from one than the other and complete neutralization willnot be obtained.

In carrying my invention into effect, I provide means whereby thecapacities to ground of two conductors may be balanced in such a waythat radiation of high frequency energy will be prevented.

llhe novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims.

My invention itself, however, both as to itsorganization and method ofoperation will best be understood by reference to the followingspecification taken in connection with the accompanying drawing in whichFig. 1 shows diagrammatically a circuit arrangement which may be used incarrying my invention into effect; Figs. 2 and?) show modifications inthe circuit arrangement; and Fig. 4 is a partially diagrammatic view ofa transformer which is specially suitable for use in connection with myinvention together with a portion of the circuit connections which maybe employed therewith.

I have indicated in Fig. l'low tension supply conductors 1 for supplyingcurrent to the primary 2 of a step-up transformer 3. The secondarywinding 4 of this transformer is connected by the leads 5 to theelectrodes -6 of a discharge gap. .Variable condensers 7 and 8 areconnected between each of the supply conductors 5 and ground at 9. Byadjusting the relative capacities of condensers 7 and 8 I have foundthat the system may be balanced in such a way that substantially noradiation of high frequency energy from the conductors 5 will beproduced. I have found in fact that the system may be so adjusted that avery sensitive radio receiving set may be operated within a few feet ofthe conductors 5 without any disturbance whatever.

Choke coils'10 are preferably provided in the low tension circult toprevent any high frequency currents which are transmitted through thetransformer from flowing out condensers 7 and 8 to ground, serve to bal'ance and render electrically symmetrical the ignition circuit 5, 5, 6,so that the high-frequency pulsations radiated from one side of the saidcircuit are exactly balanced and neutralized by the pulsations radiatedfrom the other side of the spark-gap or ignition circuit. The termelectrically symmetrical is employed to designate a condition of circuitin which each side thereof has precisely the same electricalcharacteristics. Under this condition. it is apparent that the phases ofthe high-frequency oscillationsradlatcd from opposite sides of the line,as stated hereinbefore, would be displaced from one another 180 and assuch, would be completely balanced or neutralized in so far asdisturbing effects on neighboring radio sets and other delicatelyresponsive impulse receiving apparatus, are concerned. In practice, itgenerally happens that the electrical characteristics of each side ofthe circuit 1, 10, 10 connected back to the source of energy to ground,is so greatly unequal and out of balance, which may be caused, forexample,

by faulty design of the generator, as to render it virtually impossiblefor condensers 7 and 8, preferably of a commercial size' and type, torestore and maintain an overall symmetry of the entire circuit 1, 10, 5,6, 5, 10, 1. In that event, it may be necessary to separate, as far aspossible, the source of energy portion of the circuit from the spark-gapor load portion and this may be conveniently accomplished byinterpositioning a transformer between the respective portions of thecircuit. The same transformer which provides the step-up voltage mayalso serve to isolate the two portions of the circuit to a sufiicientdegree whereby 'the secondary circuit may be rendered substantiallysymmetrical irrespective of the electrical constants of the primarycircuit. When a transformer or other circuit-separating member isemployed, the condensers 7 and 8 are called upon to balance and produceelectrical symmetry only in the secondary circuit, 5, 5, 6, although itis to be understood that the separation of the circuits is merely anexpedient method of obtaining the proper balance of circuitcharacteristics without the necessity of employing unusually largebalancing elements and if desired, I may obtain symmetry of the entirecircuit 1, 10, 5, 6, 5, 10, 1 by suitable means. From the foregoing, itwill also be evident, that even if the potential of the source of energyis sufiiciently high, as not to require avoltage step-up device, which,

however, is contrary to the usual practice, it may still be desirable toemploy a transformer of unity transformation in order to obtain theseparation of circuits referred to hereinbefore and conv rsely, ifbalancing means of effective des gn be employed, it may be expedient todispense entirely with the transformer under conditions of a highpotential source of energy. It is apparent that the condensers 7 and 8do not constitute a filtering arrangement in the sense of frequencydiscrimination and thus they do not perform the same function as theelements 11, 11 of the primary circuit but instead, lend reactivecharacteristics to each side of the circuit to the end that the highfrequency radiating portions of the ignition system may be renderedsymmetrical; obviously the condensers 7 and 8 may or may not be adjustedto the same value of react-ance.

In view of the difiiculty of making variable condensers adapted to beconnected direetly to high tension lines 5, it may be desirable toemploy specially constructed coupling condensers 13 between theconductors 5 and the variable condensers 7 and 8, as indicated in Fig. 2of the drawing. Also since the desired adjustment is one of relativecapacity between the two conductors 5and ground, the. condensers 7 and 8ma be combined, as shown in Fig. 3, in a smgle unit 14, comprising twofixed condenser electrodes 15 and 16, and one movable electrode 17,which is so arranged that it may be moved relatively to the fixedelectrodes 15 and 16.

InFig. 4, I have shown, a transformer which is especially adapted foruse in connection with my invention. This comprises,

a low tension winding 18, and a hi h tension winding 19, both wound on te central core 20 of a shell type transformer. Between the two windingsof the transformer is interposed a ma netic shunt 21. Short air gaps 22are p're erably provided between the ends of the shunt 21 and the outerlegs of the transformer core, to prevent a short circuiting of the lowfrequency magnetic flux of the transformer. This shunt is effective inshort circuiting a large portion of the high frequency flux, and as aresult, the amount of high fre uency energy transferred through thetrans ormer to the low tension side is greatly reduced. The particularform of transformer used forms no part of my present invention, but isdescribed and claimed in a copending a plication of Edward A. \Vagner,Serial 0. 115,790 filed June 14, 1926.

A convenient method of formin the coupling condensers 13 illustrated inigs. 2 and 3 of the drawing, is shown in connection with Fig. 4. Each ofthe high tension leads 5 is surrounded by the usual insulating material23, and a metal sheath 24 is wound around the insulating conductor for aportion of its length, thus forming an electrode of the couplingcondenser, the conductors themselves forming the other electrode. Theseconducting sheaths 2 f are connected to fixed plates 15 and 16, of thevariable condensers and a movable plate 17 is located in such a way thatas it is moved the relative capacities of the two condensers may bevaried.

While I have shown and described the preferred embodiments of myinvention, it will be apparent that many modifications in the precisemanner in which it is carried into effect may be made without departingfrom the scope thereof, as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent 7f the UnitedStates, is,-

1. The combination in an ignition system of a discharge gap, a step-uptransformer for supplying a high potential to said gap to produce adischarge, and means for balancing the capacity to earth of theconductors connecting said transformer and said gap to prevent radiationof high frequency energy from said conductors.

2. The combination in an ignition system of a discharge gap, a step-uptransformer for supplying a high potential to said gap to produce adischarge, a pair of conductors connecting said transformer and saidgap, a pair of condensers connecting said conduc tors to ground, andmeans for adjusting the relative capacities of said condensers to prevent radiation of high frequency energy from said conductors.

3. The combination in an ignition system of a discharge gap, a step-uptransformer for supplying a high potential to said gap to produce adischarge, a pair of insulated conductors connecting said transformerand said gap, a conducting sheath surrounding each of said insulatedconductors for a portion of its length, a condenser connected betweeneach of said conducting sheaths and ground, and means for varying therelative capacities of said condensers.

4. The combination in an ignition system of a discharge gap, a step-uptransformer for supplying a hlgh potential to said gap to produce adischarge, a pair of insulated conductors connecting said transformerand said gap, a conducting sheath surrounding each of said insulatedconductors for a portion of its length, a condenser electrode connectedto each of said conducting sheaths and an adjustable grounded condenserelectrode in capacitative relation to both of said first mentionedcondenser electrodes.

5. The combination in an ignition system of a discharge gap, anenergizing circuit for producing a spark discharge across the gapwhereby unbalanced high fre uency energy normally would be radiated romone side of the circuit and means for equalizing the paths from bothsides of said circuit to ground whereby the radiation of high frequencyenergy is prevented, said means comprising reactance elements.

In witness whereof, I have hereunto set my hand this 11th day of June,1926.

ERNST F. W. ALEXANDERSON.

